Patent Grant
9296185
Many products, such as wall panels, wall coverings, and decorative tiles, are made of a wide variety of materials. These materials include corrugated paper, textiles, glass, glass fiber, metals (such as tin, steel, and aluminum), ceramics (such as porcelain), wood, and plastics. For many of these products some of these materials have good mechanical properties and surface quality; some are inexpensive and affordable; and some are highly resistant to mold and/or mildew.
Unfortunately, though, for many products none of these materials individually have good mechanical properties, good surface qualities, is inexpensive, and highly resistant to mold and mildew. In addition, many of these materials have other drawbacks. For example, many include chemical additives such as, volatile organic compounds (VOCs), that can be harmful to people and/or the environment. Many do not provide good thermal insulation, which can cause excessive energy consumption. Many are not easily recyclable. And, many are not lightweight, and thus, require more energy to transport and stronger structures to support and hold the products during use.
A possible alternative to such materials are thermoplastic polymers because they are inexpensive, highly resistant to mold and/or mildew, and can be easily formed into shapes that can provide good mechanical properties when subjected to a particular loading, and can be made to have a good surface quality. Thermoplastic polymers can also be made very light by foaming them to generate a material structure that includes many cells, and they can be easily recycled.
Thermoplastic polymers are frequently manufactured in thin sheets that are then wound around a spool. When manufactured in this manner, the thin sheet is typically used to make components that are also thin. When such a sheet is used to make a component that is thicker than the sheet, the sheet is cut into sections and then each section is joined to the other sections to form a laminate. Adhesion bonding and/or fusion bonding typically join the sections together. Adhesion bonding includes applying an adhesive to a surface of a section and then pressing the two sections together while the adhesive cures. Fusion bonding includes melting a surface of both sections, and then pressing the sections together while the two molten surfaces coalesce. Then the coalesced surfaces are cooled to solidify them as one material.
Unfortunately, adhesion bonding typically releases VOCs as the adhesive cures, and fusion bonding requires very delicate control of the process to maintain the general shape of the laminate as the surfaces are melted, coalesce, and solidify.
In an aspect of the invention, a method for joining two components includes positioning a thermoplastic polymer portion of a first component adjacent a thermoplastic polymer portion of a second component such that the first and second portions form an interface. At least one of the portions includes a microstructure having a plurality of closed cells, each cell containing a void and each cell having a maximum dimension extending across the void within the cell that ranges between 1 micrometer and 200 micrometers long. The method also includes exerting pressure on the thermoplastic polymer portions to form a bond at the interface that holds the portions together. The plurality of closed cells, and especially those adjacent the surface of the thermoplastic polymer portion that form the interface, help isolate thermally and/or chemically the surface from the remainder of the portion, and thus allow the surface of the portion to exist in a molten and/or dissolved state while the remainder of the portion exists in a more solid state. With the remainder of the thermoplastic polymer portion in the solid state, the portion can withstand the pressure exerted on the thermoplastic polymer portions while the bond forms, without deforming the general shape of the portion.
In another aspect of the invention such a method also includes generating pressure inside a plurality of the closed cells to help the cells resist the pressure exerted on the thermoplastic polymer portion while the bond forms at the interface. By resisting the pressure exerted on the portion in this manner, the portion can more easily withstand the pressure exerted on the thermoplastic polymer portions while the bond forms, without deforming the general shape of the portion.
In the first step 20 of the process, a thermoplastic polymer portion of a first component (not shown in
In this and other embodiments of the process, the process also includes a step 24 in which the interface-forming surface of the thermoplastic polymer portion having the plurality of closed cells is heated to a temperature that causes the surface to melt. In this and other embodiments, the thermoplastic polymer portion includes a skin (shown and discussed in greater detail in conjunction with
Other embodiments are possible. For example, both surfaces may be heated to facilitate their coalescence. As another example, the interface-forming surface of the thermoplastic polymer portion having the plurality of closed cells may be heated to a temperature substantially below the melting point of the surface to facilitate the formation of an adhesion bond. As another example, the interface-forming surface may not include a skin and instead may be defined by the walls of the cells disposed at and immediately adjacent the face of the thermoplastic polymer portion. In such an example, heat may be applied to the cells immediately adjacent the face to melt the cells in preparation for forming a fusion bond.
In this and other embodiments of the process, the process also includes a step 28 in which pressure inside a plurality of the closed cells—in the voids of the closed cells—is generated to help the cells resist the pressure exerted on the thermoplastic polymer portion while the bond forms at the interface. By resisting the pressure exerted on the portion in this manner, the portion can more easily withstand the pressure exerted on the thermoplastic polymer portions while the bond forms, without deforming the general shape of the portion. Pressure inside a plurality of the closed cells also allows more pressure to be exerted on the thermoplastic polymer portions to form the bond at the interface. In this and other embodiments, the pressure inside the closed cells may be generated as the closed cells are created in the thermoplastic polymer portion (discussed in greater detail in conjunction with
In this and other embodiments, the panel 44 includes a fusion bond 46 that is about 40 μm (about 0.0016 inches) thick. The fusion bond 46 is formed by material in the interface-forming surface of each of the sheets 40 and 42 melting, coalescing, and then hardening. Because of this, the amount, continuity and heat transfer characteristics of the material in each of the interface-forming surfaces affects the process for forming a good quality fusion band joining the two sheets 40 and 42. To obtain a quality, strong bond in the panel 44, a skin (shown and discussed in conjunction with
In this and other embodiments of the panel 44, each of the thermoplastic polymer sheets 40 and 42 is about 500 μm (about 0.02 inches) thick, and includes recycled polyethylene terephthalate (RPET). In addition, each of the sheets 40 and 42 includes a microstructure that includes many closed cells 48 (only 6 labeled in
With the closed-cell microstructure of each of the sheets 40 and 42 thermally isolating the interface-forming surface of each of the sheets, one can heat the skin of each sheet to the interface-forming surface's melting temperature without causing the remainder of the sheet underneath the skin to melt. Thus, the microstructure of the panel 44 can retain the microstructure of each of the sheets 40 and 42 before the sheets are fused together. Thus, a panel 44 can be formed whose thickness can be dimensionally precise and consistent without substantial processing after the sheets 40 and 42 are joined. In addition, confining to the skin much of the heat required to melt the skin, the thickness of each of the sheets 40 and 42 may be small and thus quickly and easily manufactured.
Still referring to
Other embodiments are possible. For example, three or more sheets 40 and 42 may be fused together to form a panel 44. As other examples, each of the sheets 40 and 42 may include different microstructures, such as larger or smaller closed cells than the other sheet, or different numbers and/or distributions of the closed cells in each of the sheets 40 and 42, and/or within a single sheet. Also, each of the sheets 40 and 42 may have a thickness that is different than the other sheet, and/or a density (mass of material per unit volume) that is different than the other sheet, to produce a panel 44 having any desired thickness. In addition, one or more sheets 40 and 42 may be fused together with one or more sheets of a thermoplastic polymer sheet having a solid microstructure to produce a denser panel. The solid thermoplastic sheets and the thermoplastic sheets having a closed-cell microstructure may be arranged as desired. For example, they can be fused together alternating solid and closed-cell sheets, or sandwiching one or more closed-cell sheets in between solid thermoplastic sheets. This assemblage of solid thermoplastic and expanded microcellular materials allows one to exploit the mechanical strength of a solid thermoplastic and the insulation and lightweight qualities of a closed-cell thermoplastic sheet.
In this and other embodiments, each of the sheets 52 and 54 are pulled off one of the respective rolls 64 and 66 of the thermoplastic polymer material, and the surfaces 60 and 62 are heated by one of the respective electrically heated rollers 68 and 70. In other embodiments, each of the surfaces 60 and 62 may be heated by infrared heat, hot air, or any other desired method for heating a surface. After the surfaces 60 and 62 begin to melt, the sheets 52 and 54 are directed toward each other to position the surfaces 60 and 62 adjacent each other. When the two surfaces 60 and 62 are adjacent each other, they form an interface. Once the interface is formed, both sheets 52 and 54 are inserted, together, between two nip rollers 72 and 74 that exert pressure on a portion of the sheets 52 and 54 by pinching the portion. As the portion of the sheets 52 and 54 is pinched by the rollers 72 and 74, a bond between the two surfaces 60 and 62 begins to form at the interface in the portion and continues to form after the portion has been pinched and no longer between the rollers 72 and 74. If the bond is an adhesion bond, then the adhesive cures; if the bond is a fusion bond then the molten interface solidifies. To facilitate the completion of the bond and thus speed up the formation of the panel 56, the interface may subsequently be kept warm to promote the curing of the adhesive, or cooled to promote the solidification of the interface.
During the bonding process, excessive heat and/or pressure can damage the microstructure of each of the sheets 40 and 42 by collapsing or crushing one or more of the closed cells—densification of the microstructure. To help prevent this, pressure 80 (labeled in only two of the closed cells 48 for clarity) may be generated inside a plurality of the closed cells 48. If the gas pressure inside the closed cells is equal to or greater than the force 82 divided by the area of each sheet 40 and 42 that the force 82 is applied to, then the force 82 exerted on the sheets 40 and 42 to form the bond 46 will not crush most of the closed cells 48. Some of the closed cells 48 close to the interface-forming surfaces of the sheets 40 and 42, are warmed as the surfaces are heated to a molten state and thus not able to resist the pressure generated by the force 82.
In this and other embodiments, the pressure 80 may be generated as the microstructure is formed in each of the sheets 40 and 42 (shown and discussed in greater detail in conjunction with
Because the gas has to migrate through the solid portions of the sheet to exit the sheet, it takes time for the sheet and the amount of dissolved gas within it to reach an equilibrium. Thus, it takes time for the pressure that is generated inside the closed cells 48 as the closed cells 48 are generated in the sheets 40 and 42, to equalize with the pressure surrounding the sheets 40 and 42. And thus, one can join the sheets 40 and 42 as discussed elsewhere herein, before the pressure generated inside the closed cells 48 equalizes with the surrounding environment.
The time that it takes for the pressure generated inside the closed cells 48 to equalize with the surrounding environment depends on any number of factors, such as the crystallinity of the sheets 40 and 42, the amount of solid material in the sheets 40 and 42, and the initial gas concentration in the sheets. These factors can be manipulated to provide any desired period. For example, increasing the amount of solid material that the gas has to migrate through to exit the sheet will increase the duration of the period. Thus, generating a skin as discussed in greater detail in conjunction with
Referring to
Referring to
In the process, the first step 102 is to dissolve into the polymer 90 any desired gas 98 that does not react with the polymer 90. For example, in this and certain other embodiments of the process, the gas 98 may be carbon dioxide (CO2) because CO2 is abundant, inexpensive, and does not react with PET. In other embodiments of the process, the gas may be nitrogen and/or helium. Dissolving the gas 98 into the polymer 90 may be accomplished by exposing the polymer for a period of time to an atmosphere of the gas 98 having a temperature and a pressure. The temperature, pressure, and period of time may be any desired temperature, pressure, and period of time to dissolve the desired amount of gas 98 into the polymer 90. The amount of gas 98 dissolved into the polymer 90 is directly proportional to the pressure of the gas 98 and the period of time that the polymer 90 is exposed to the gas 98 at a specific temperature and specific pressure, but is inversely proportional to the temperature of gas 98. For example, in this and certain other embodiments, the temperature may be 72° Fahrenheit, the pressure may be 725 pounds per square inch (psi), and the duration of the period may be 10 hours. This typically saturates the polymer 90 with the gas 98. In other embodiments, the pressure may range between 500 psi and 1000 psi, and the duration of the period may range between 4 hours and 24 hours.
Because the layers of the rolled polymer film 90 that lie between adjacent layers or between a layer and the drum 96 are substantially unexposed to the atmosphere when the roll is placed in the atmosphere, a material 104 is interleaved between each layer of the rolled polymer film that exposes each layer to the atmosphere. In this and certain other embodiments, the material 104 includes a sheet of cellulose, and is disposed between each layer of the polymer film 90 by merging the sheet with the film and then rolling the combination into a single roll 106. The material 104 exposes each layer of the polymer film 90 by allowing the gas to easily pass through it. After the gas 98 has saturated the polymer film 90, the material 104 may be removed from the roll 106 and saved as a roll 108 for re-use.
The next step 110 in the process includes exposing the polymer film 90 with the dissolved gas 98 to an atmosphere having less pressure than the one in the first step to cause the combination of the polymer film 90 and the gas 98 dissolved in the polymer film 90 to become thermodynamically unstable—i.e. the whole polymer or regions of the polymer to become supersaturated with the dissolved gas 98. For example, in this and certain other embodiments, the reduction in pressure may be accomplished by simply exposing the polymer film 90 to atmospheric pressure, which is about 14.7 psi, in the ambient environment.
When the combination of the polymer film 90 and the dissolved gas 98 becomes thermodynamically unstable, the dissolved gas tries to migrate out of the film 90 and into the ambient environment surrounding the film 90. Because the dissolved gas in the interior regions of the polymer film 90 must migrate through the regions of the polymer film 90 that are closer to the film's surface to escape from the polymer film 90, the dissolved gas in the interior regions begins to migrate after the dissolved gas in the surface regions begins to migrate, and takes more time to reach the ambient environment surrounding the polymer film 90 than the dissolved gas 98 in the film's regions that is closer to the film's surface. Thus, before heating the polymer film 90 to a temperature that is or is close to its glass transition temperature, one can modify the concentration of dissolved gas 98 in regions of the polymer film 90 by exposing the polymer film 90 to an atmosphere having less pressure than the one in the first step for a period of time. Because the concentration of dissolved gas 98 depends on the amount of gas that escapes into the ambient environment surrounding the polymer film 90, the concentration of dissolved gas 98 is inversely proportional to the period of time that the film 90 is exposed to the low-pressure atmosphere before being heated to its or close to its glass transition temperature.
In this manner, a skin, such as the skin 94 (
The next step 112 in the process is to nucleate and grow bubbles 100 (
To heat the polymer film 90 that includes the dissolved gas 98, one may use any desired heating apparatus. For example, in this and certain other embodiments, the PET film may be heated by a roll fed flotation/impingement oven, disclosed in the currently pending U.S. patent application Ser. No. 12/423,790, titled ROLL FED FLOTATION/IMPINGEMENT AIR OVENS AND RELATED THERMOFORMING SYSTEMS FOR CORRUGATION-FREE HEATING AND EXPANDING OF GAS IMPREGNATED THERMOPLASTIC WEBS, filed 14 Apr. 2009, and incorporated herein by this reference. This oven suspends and heats a polymer film that moves through the oven, without restricting the expansion of the film.
The next step 114 in the process includes reducing the temperature of the heated polymer 90, and thus the malleability of the polymer 90 that occurs at or near the glass transition temperature, to stop the growth of the bubbles 100. The temperature of the heated polymer may be reduced using any desired technique. For example, in this and certain other embodiments, the polymer film 90 may be left to cool at ambient room temperature—i.e. simply removed from the heating apparatus. In other embodiments the heated polymer film 90 may be quenched by drenching it with cold water, cold air, or any other desired medium.
Other embodiments of the process are possible. For example, the polymer film 90 can be heated to a temperature that is or close to its glass transition temperature when the polymer film 90 is initially exposed to an atmosphere that causes the gas dissolved in the polymer film 90 to become thermodynamically unstable. This allows one to make a film that does not include a skin or includes a skin having a minimal thickness.
The preceding discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
This application claims priority from commonly owned U.S. Provisional Patent Application 61/342,752 filed 19 Apr. 2010, and titled “A Panel That Includes An Expanded Microcelluar Material, And Related Methods For Making And Using The Same”, which is incorporated by reference.
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| PCT/US2011/033075 | 4/19/2011 | WO | 00 | 10/11/2012 |
| Publishing Document | Publishing Date | Country | Kind |
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| WO2011/133568 | 10/27/2011 | WO | A |
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| Number | Date | Country | |
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| 61342752 | Apr 2010 | US |
